Self-aligned contact areas for sidewall image transfer formed conductors

ABSTRACT

A method and structure for forming a sidewall image transfer conductor having a contact pad includes forming an insulator to include a recess, depositing a conductor around the insulator, and etching the conductor to form the sidewall image transfer conductor, wherein the conductor remains in the recess and forms the contact pad and the recess is perpendicular to the sidewall image transfer conductor.

RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.09/379.453, filed Aug. 23, 1999 now U.S. Pat. No. 6,566,759.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to contacts for integratedcircuit devices and more particularly to improved landing pads forcontacts for self-aligned sidewall image conductors.

2. Description of the Related Art

Sidewall Image Transfer (SIT) techniques form conductors with verynarrow widths or semiconductor devices with very short gate lengthswithout using critical photolithography. For example, a top view of acontact opening 10 for a sidewall conductor 11 is shown in FIG. 1A andcross-sectional views at different points along the same structure areshown in FIGS. 1B and 1C. More specifically, FIG. 1B is a cross-sectionof FIG. 1A along line A-A′ and FIG. 1C is a cross-section of FIG. 1Aalong line B-B′.

In sidewall image transfer technology, conductive sidewalls 11 areformed adjacent an insulating mandrel 12. More specifically, theinsulator 12 (such as a glass or oxide) is formed using conventionallithographic techniques including depositing and patterning. Thesidewall spacer conductors 11 are formed using conventional depositionand directional etching techniques (e.g., reactive ion etching—RIE), asis well known to those ordinarily skilled in the art. More specifically,a conductor (such as metal, alloy or polysilicon) is deposited tosurround and cover the insulator 12. Then, a directional etch is appliedto the conductor. The directional etch removes material from horizontalsurfaces at a much faster rate that it removes material from verticalsurfaces, thereby leaving sidewall spacers 11, as shown in FIG. 1B. Thedirectional etch could be, for example, a reactive ion etching processwhich is selective to the conductor and does not affect the insulator 12or the underlying substrate.

The insulator 12 can be formed to have a minimum lithographic size whichallows the conductive spacers 11 to be formed at sub-lithographic sizes.FIG. 1A also illustrates trim areas 13 which will eventually be removedto permit separation of the distinct conductors 11.

Openings 10 into an insulator 14 are made using standard lithographic orother similar techniques. The openings 10 will eventually be filled witha conductive material to allow contact to an upper layer of wiring whichwill be formed at a later processing step.

However, the contact opening 10 must be small because the sidewallconductor 11 is very narrow (e.g., possibly sub-lithographic). Thismakes the alignment and overlay process very difficult, which in turndecreases yield and imposes limits on the pitch of structures so formed.Therefore, there is in a need for an improved structure and system forforming contacts to sidewall image transfer conductors.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide astructure and method for forming a sidewall image transfer conductorhaving a contact pad that includes forming an insulator to include arecess, depositing a conductor around the insulator, and etching theconductor to form the sidewall image transfer conductor. The conductorremains in the recess and forms the contact pad. The recess isperpendicular to the sidewall image transfer conductor. The recess isformed to have a width smaller than twice a thickness of the sidewallimage transfer conductor. The contact pad is formed to have a widthgreater than that of the sidewall image transfer conductor. The recessincludes an indent and/or two outdents. The contact pad is formed tohave an upper surface planar with that of the insulator and the sidewallimage transfer conductor and a uniform unsloped upper surface.

Another embodiment of the invention is an integrated circuit chip thatincludes an insulator having a recess, a sidewall conductor positionedalong the insulator, and a contact pad in the recess (the recess isperpendicular to said sidewall conductor). The recess has a widthsmaller than twice a thickness of the sidewall conductor. The contactpad has a width greater than that of the sidewall conductor. The recessincludes an indent and/or two outdents. The contact pad has a uniformunsloped upper surface planar with that of the insulator and thesidewall conductor.

Yet another embodiment of the invention is an integrated circuit chipthat includes an insulating mandrel having a linear edge and anon-linear feature along the linear edge, and a sidewall conductorpositioned along the linear edge and the non-linear feature. Thesidewall conductor within the non-linear feature includes a contact padfor the sidewall conductor. The non-linear feature has a width smallerthan twice a thickness of the sidewall conductor. The contact pad has awidth greater than that of the sidewall conductor. The non-linearfeature is either a rectangular indent, two outdents, a curved indent ora wedge. The contact pad has a uniform unsloped upper surface planarwith that of the insulator and the sidewall image transfer conductor.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, aspects and advantages will be betterunderstood from the following detailed description of a preferredembodiment of the invention with reference to the drawings, in which:

FIGS. 1A-1C are schematic diagrams of top and side views of conventionalsidewall image transfer conductors and contact openings;

FIGS. 2A-2B are schematic diagrams of top and side views of sidewallimage transfer conductors, contact openings and lithographically formedcontact pads according to the invention;

FIGS. 3A-3C are schematic diagrams of side and top views of sidewallimage transfer conductors and contact openings according to theinvention; and

FIG. 4 is a flow diagram illustrating a preferred method of theinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

As mentioned above, in sidewall image transfer technologies, the contactopening 10 must be small because the sidewall conductor 11 is verynarrow. This makes the alignment and overlay process very difficult.

One solution to the above problem is to form a large contact pad 26 overthe portion of sidewall conductor where the contact opening 20 will beformed, as shown in FIGS. 2A and 2B. More specifically, FIG. 2Aillustrates sidewall conductors 21 formed along an insulator 22 in astructure which is substantially similar to the that shown in FIGS.1A-1C. However, FIG. 2A also illustrates mask openings 25 that are usedto form the contact pads 26.

The mask and openings 25 are formed using conventional methods, such ascommon lithographic masking techniques. The contact pads 26 are formedby depositing a conductor into the mask openings 25. The insulator 24 isthen deposited and contact openings 20 are formed as discussed above,using conventional methods, such as lithography or laser oblation.

The contact pads 26 provide a larger area onto which land the contactopenings 20. The relatively large area of the contact pad 26 increasesthe likelihood that the opening 20 will be properly aligned with thecontact pad 26, which increases manufacturing yield. However, theformation of the contact pad 26 requires the additional steps associatedwith forming and removing the mask and with depositing the conductivematerial for the contact pad 26. Therefore, while the likelihood ofaligning the contact opening 20 and the contact pad 26 is increased withthis method, the complexity of the manufacturing process is alsoincreased.

Further, the contact 26 itself has an irregular typography (as shown inFIG. 2B) because the contact pad 26 is formed over the corner of theinsulator 22 and a portion of the conductive spacer 21. The irregulartypography decreases the likelihood of forming a good electricalconnection between the contact pad 26 and the conductive stud which willeventually fill the opening 20. Also, the contract pads 26 increase theoverall size of the device which limits device density, increasesmanufacturing costs, decreases processing speed, etc.

A second embodiment of the invention, shown in FIGS. 3A-3C, increasesthe size of the conductive spacer 21 in the area where the contactopening 20 will be formed, without the additional processing steps andchip area consumption required with the formation of the contact pads 26discussed above.

More specifically, in this embodiment of the invention, the shape of theinsulator 22 is altered in the areas where the contact openings 20 willbe formed. The shape is altered to include a feature such as an indent34 or two out-dents 33 (or both as shown in the Figures). FIG. 3C alsoillustrates other wiring levels 36 within the structure.

The indent 34 makes the sidewall conductor 21 substantially wider andforms a contact pad 32. More specifically, the indent 34 creates anincrease in sidewall area which allows a sufficient amount of conductivespacer material to accumulate to form a contact pad 32. Therefore,during the directional etching process mentioned in the Backgroundsection, the shape of the spacer 34 allows the conductive material toremain in the indent 34, thereby forming the contact pad 32.

As shown in cross-section in FIG. 3B, the contact pad 32 of the sidewallconductor 21 is substantially larger in the area where the indent 34 islocated. As with the previous embodiment, by increasing the size of theconductive spacer 21 in the contact pad 32 area, the likelihood ofhaving the contact opening 20 aligned with the contact pad 32 issubstantially increased.

Further, the invention avoids the problems associated with the previousembodiment by only altering the shape of the insulating mandrel 22.Therefore, this embodiment produces a self-aligned contact pad 32 anddoes not require the additional processing steps which are required toform the contact pad 26. Further, the contact pad 32 has a substantiallyunsloped planar topography which increases the likelihood that a goodelectrical connection will be made between the stud which eventuallyfills the opening 20 and the sidewall spacer 21.

The indent 34 is sized such that the conductor deposited over themandrel 22 completely fills in the indented shape 34. The width of thepad 32 is preferrably less than or equal to two times the sidewallconductor 21 thickness (since the indent 34 fills from both sides) toensure that the contact pad has a substantally uniform unsloped uppersurface. When the conductive sidewall etch is performed, the contact padarea 32 will form the relatively flat-topped structure 32, rather thanthe sloped, narrow surface of the sidewall spacer 11 (e.g., FIG. 1B)that is the natural product of this process. Since the conductor 21 isexposed to the etching rather than protected from it by a photoresist,the shape of the resulting top of the contact landing area 32 is planaror recessed relative to the top of the mandrel 22. As explained above,this flat or recessed shape increases the likelihood of a goodelectrical contact with the conductive stud which will fill the contactopening 20.

A flowchart representation of the invention is illustrated in FIG. 4. Asshown in item 40, an insulator 22 including a recess 34 is formed. Initem 41, a conductor 21 is deposited around the insulator 22. In item42, The conductor 21 is etched to form the sidewall image transferconductor 21, wherein the conductor 21 remains in the recess 34 andforms the contact pad 32.

The foregoing example uses an indent 34 to create the contact pad 32.However, as would be known by one ordinarily skilled in the art giventhis disclosure, any non-linear feature on the insulating mandrel 22,such as a curved opening, a wedge, etc. could be used depending upon thespecific design goals.

While the invention has been discussed above with respect to aparticular mandrel 22/conductive spacer 21 combination, as would beknown by one ordinarily skilled in the art given this disclosure, theinvention can be used with any similar any SIT structure where anincrease and flatness of contact area are important. This is especiallyuseful with very short channel devices where SIT achievesub-lithographic resolutions.

As shown above, the invention incorporates a special geometric featurein the mandrel used to define the gate conductors which produces a fullyself-aligned feature suitable for use later as an area to land acontact.

While the invention has been described in terms of preferredembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theappended claims.

1. A process for forming a sidewall conductor having a contact padcomprising: forming an insulating mandrel on an upper surface of asubstrate such that said insulating mandrel has a sidewall substantiallyperpendicular to said upper surface of said substrate; forming a recessin said sidewall in a direction substantially parallel to said uppersurface of said substrate; depositing a conductor on said upper surfaceof said substrate and around said insulating mandrel, such that saidconductor is formed on said sidewall of said insulating mandrel; andetching said conductor to form said sidewall conductor along saidsidewall, wherein said conductor remains in said recess and forms saidcontact pad and said recess is perpendicular to said sidewall conductor.2. The process in claim 1, wherein said recess is formed to have a widthsmaller than twice a thickness of said sidewall conductor.
 3. Theprocess in claim 1, wherein said contact pad is formed to have a widthgreater than that of said sidewall conductor.
 4. The process in claim 1,wherein said recess comprises an indent.
 5. The process in claim 1,wherein said recess comprises two outdents.
 6. The process in claim 1,wherein said contact pad is formed to have an upper surface planar withthat of said insulator and said sidewall conductor.
 7. The process inclaim 1, wherein said contact pad is formed to have uniform unslopedupper surface.
 8. A process for forming a conductor having a contactpad, said process comprising: forming an insulating mandrel on an uppersurface of a substrate such that said insulating mandrel has a sidewallsubstantially perpendicular to said upper surface of said substrate;forming a recess in said sidewall of said insulating mandrel in adirection substantially parallel to said upper surface of saidsubstrate; depositing a conductor on said upper surface of saidsubstrate and around said insulating mandrel, such that said conductoris formed on said sidewall of said insulating mandrel; and etching saidconductor to leave said conductor along said sidewall, such that saidconductor remains in said recess and forms said contact pad.
 9. Theprocess in claim 8, wherein said recess is formed to have a widthsmaller than twice a thickness of the portion of said conductor thatremains after said etching process.
 10. The process in claim 8, whereinsaid contact pad is formed to have a width greater than that of theportion of said conductor that remains after said etching process. 11.The process in claim 8, wherein said recess comprises an indent.
 12. Theprocess in claim 8, wherein said recess comprises two outdents.
 13. Theprocess in claim 8, wherein said contact pad is formed to have an uppersurface planar with that of said insulator and said conductor.
 14. Theprocess in claim 8, wherein said contact pad is formed to have a uniformunsloped upper surface.
 15. A process for forming a conductor having acontact pad, said process comprising: forming an insulating mandrel onan upper surface of a substrate such that said insulating mandrel has asidewall substantially perpendicular to said upper surface of saidsubstrate; forming a recess in said sidewall of said insulating mandrelin a direction substantially parallel to said upper surface of saidsubstrate, wherein said recess comprises an indent in said sidewall andsaid recess is perpendicular to said sidewall; depositing a conductor onsaid upper surface of said substrate and around said insulating mandrel,such that said conductor is formed on said sidewall of said insulatingmandrel; and etching said conductor to leave said conductor along saidsidewall, such that said conductor remains in said recess and forms saidcontact pad.
 16. The process in claim 15, wherein said recess is formedto have a width smaller than twice a thickness of the portion of saidconductor that remains after said etching process.
 17. The process inclaim 15, wherein said contact pad is formed to have a width greaterthan that of the portion of said conductor that remains after saidetching process.
 18. The process in claim 15, wherein said recesscomprises two outdents.
 19. The process in claim 15, wherein saidcontact pad is formed to have an upper surface planar with that of saidinsulator and said conductor.
 20. The process in claim 15, wherein saidcontact pad is formed to have a uniform, unsloped upper surface.